Variable lift electromechanical valve actuator

ABSTRACT

A variable lift electromechanical valve actuator for use with an internal combustion engine. The electromechanical valve includes a first electromagnet, a second electromagnet, and a hydraulic lifting mechanism. The upper electromagnet is fixedly mounted to a housing while the lower electromagnet slides in conjunction with the hydraulic lifting mechanism. Multiple valve lifts are provided for by the movement of the lower electromagnetic electromagnet. Variable valve lift allows for more efficient operation of the engine and reduced power consumption, noise, vibration, and wear concerns.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to electromechanical valveactuators and more particularly to variable lift electromechanicalvalves for internal combustion engines.

[0002] Engine valves control the flow in and out of the cylinders ininternal combustion engines. Engine valves are typically controlled bycamshafts that rotate, at a speed proportional to the crankshaft causingthe valves to open and close at specified intervals. An example of atypical valve train includes a rotating camshaft having elliptical lobeswhich contact tappets or lash compensators on the valve. As theelliptical lobe presses against the tappet, the valve is pushed open atdetermined intervals, and as the elliptical lobes rotate away from thetappet, the valve is closed by a spring. The opening and closing timesof the valves are determined by the geometry of the lobes, and therelative angular position with respect to the crankshaft when the engineis assembled. Manufacturers can adjust this timing by altering theshape, size, and angular location of the elliptical lobes. However, thetiming as well as the torque curve is typically fixed at the time theengine is assembled. The amount of valve lift is also determined by thelobes on the camshaft and therefore determined when the engine isassembled. The lack of variable valve timing and variable valve liftreduces engine optimization and therefore may reduce engine efficiency.

[0003] Another problem with conventional engines is that they require athrottle body and the associated components. The throttle body restrictsair flow into the engine. One problem with using a throttle body is thatengine efficiency is reduced due to intake restrictions. When air flowsthrough the throttle body, an air pressure drop occurs across thethrottle plate. Therefore, when the intake valve opens under throttledconditions, the piston pulls in air of a lower pressure than thesurrounding atmosphere, resulting in engine inefficiencies.Manufacturers have strived to create true throttless engine operation toincrease engine efficiency as well as allow for drive-by-wire systems.

[0004] To address problems associated with traditional valves activatedby camshafts, some manufacturers have attempted to substituteelectromechanical valve actuators (also known as electromagnetic valveactuators) in place of camshafts. Generally, these electromechanicalactuators include upper and lower electromagnets that are formed fromlamination stacks and coiled wire. The electromechanical valve actuatorsalso include an armature located between the electromagnets. Thearmature generally forms a plane somewhat perpendicular to the valvestem and includes an armature stem, that passes through both the upperand lower electromagnets, in order to open or close a valve.

[0005] In operation, the electromagnets are selectively energized,creating a magnetic force to draw the armature to the energizedelectromagnet. The surface of the electromagnet which the armaturecontacts may be referred to as a pole face. As the armature moves backand forth in pole face to pole face operation, the valve is opened andclosed. Electromechanical valve actuators allow for complete control ofthe timing of every valve. Electromechanical valve actuators may alsoopen more than one valve at the same time. One problem withelectromechanical actuated valves is that as the distance between thearmature and the magnetized electromagnet decreases, the magnetic forceexponentially increases. The increase in magnetic force causes thearmature to increase in velocity as it approaches an energizedelectromagnet. The armature then impacts the electromagnet, causingnoise and vibration. Forceful contact between the armature andelectromagnet also may cause excessive wear on the components of theelectromechanical valve actuator and other engine components.

[0006] Some manufacturers have shaped the power profile supplied to thelamination stack in an effort to soften the impact, but this mayincrease the time it takes the armature to travel from pole face to poleface. An increase in time to travel from pole face to pole faceincreases the transition times and may prevent the engine from operatingproperly because the valve cannot open and close fast enough.

[0007] At idle speeds, electromechanical valves may consume asignificant portion of power to overcome the springs in the system, andmove the armature from the pole face to pole face. Enough power must beapplied to the electromagnet to overcome any exhaust pressure in thecylinder during the opening of an exhaust valve, which creates a largedraw on the electrical system of the engine at idle speeds. The springsmay be sized to accommodate desired valve transition times as well asprovide enough force to open against any exhaust pressure. Anotherproblem with electromechanical valves is that they are not capable ofoperating throttless in all engine conditions. For manyelectromechanical valves, varying the valve timing still leaves largeregions at mid to high flow regimes where they are not able to operate.These voids in operating conditions many times occur in the mostdesirable operating regions of the engine. Yet another problem is thatelectromechanical valves are not as efficient as they can be, becausethe valve lift or how far the valves open can not be changed. Valve liftis generally set by operating conditions that demand maximum flow, whichcause inefficient engine operation in low flow conditions.

[0008] To solve some of the problems associated with electromechanicalvalves, a few manufacturers have varied the lift of the valves. Varyingthe lift of the valves may help increase the efficiency of the engine byallowing the lift of the valve to match the operating conditions.Reduced valve lift at idle conditions also helps to reduce noise,vibration, power consumption, and wear concerns.

[0009] A disadvantage some of these systems have is that the valve hasonly two lift positions, a high and a low position. The inability toadjust the lift throughout the range reduces the optimization of engineoperation associated with variable lift and can prevent maximum engineefficiency from being obtained. Another problem with some of thesesystems is that the spring bias may be offset as the valve lift ischanged which may cause the armature plate, when at rest, such as whenthe valve actuator is unpowered and no magnetic force is applied, to beoff center between the lamination stacks. During operation, this biasmay cause the armature to be more forcefully attracted to one pole face,causing noise and vibration. This bias may also make it difficult to beattracted to the other electromechanical plate, thereby requiringadditional power.

[0010] Another system addresses some of these problems by providing arange of variable lifts. The problem with this variable valve liftsystem is that it is difficult to accurately determine the lift of thevalve. The lash in the system may make it even more difficult. Due tothe type of and amount of moving parts, the inaccuracy of the systemonly increases with use. Yet another problem with this system is theincrease in moving parts, including the use of an additional motor maydecrease the reliability of the system over time.

SUMMARY OF THE INVENTION

[0011] The aforementioned problems are overcome in the present inventionwhere an electromechanical valve includes an actuator that adjusts thelower magnet, varying the valve lift, along with the armature springseat, varying the bias and spring forces, throughout a range ofadjustment. More specifically, the present invention includes a variablelift actuator in conjunction with an electromechanical valve, providingvariable valve lift while centering the armature in all lift positionsbetween the two electromagnets and reducing the impact forces of thearmature against the electromagnets during pole face to pole faceoperation.

[0012] A hydraulic actuator is used to vary the lift of the valve,allowing for maximum engine efficiency by allowing a range of flowdepending on the engine requirements, in addition to variable valvetiming. The present invention allows true throttless operation throughits entire engine speed and load ranges. The valve lift can control theair flow, eliminating the need for a throttle body. Variable valve liftand variable timing allow the engine to provide optimum torque at allrpms, unlike some electromechanical valves, which have gaps in the rpmpower band where the engine can not function properly withoutthrottling. Another benefit of the hydraulic actuator providing variablevalve lift is that a hydraulic pocket also provides a dampening means,which may reduce impact noise and wear concerns. The present inventionalso allows complete pole face to pole face movement of the armature nomatter what lift is being used. Complete pole face to pole faceoperation also helps accurately determine the amount of valve lift.Variable valve lift also reduces the spring force thereby reducing noiseand wear concerns, as well as reduces the power required to hold thearmature against either pole face, especially during engine operationwith reduced valve lift. Variable valve lift combined with variablevalve timing allows for efficient engine operation and minimal energyconsumption.

[0013] Further scope of applicability of the present invention willbecome apparent from the following detailed description, claims, anddrawings. However, it should be understood that the detailed descriptionand specific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will become more fully understood from thedetailed description given below, the appended claims, and theaccompanying drawings in which:

[0015]FIG. 1 is a sectional view of an engine valve assembly with thevalve shown in the fully closed position with reduced lift;

[0016]FIG. 2 is a sectional view similar to FIG. 1 but with the valveshown in its middle position with reduced lift;

[0017]FIG. 3 is a sectional view similar to FIG. 1 but with the valveshown in the open position with reduced lift;

[0018]FIG. 4 is a sectional view similar to FIG. 1 but with the valvebeing in the closed position with full lift;

[0019]FIG. 5 is a sectional view similar to FIG. 3 showing the valve ina open position set in the mode for full lift; and

[0020]FIG. 6 is a block diagram of the engine valve assembly and controlsystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021]FIG. 1 illustrates an electromechanical valve actuator assembly 10which is mounted on an internal combustion engine to open and close thevalves (e.g., intake or exhaust valves).

[0022] The electromechanical valve assembly 10 is generally mounted onthe cylinder head 12 of the internal combustion engine. While thecylinder head 12 may be formed in a variety of shapes andconfigurations, it typically includes a port 14, a valve seat 16, and avalve guide 18. The port 14 may be an intake or an exhaust portdepending on the function of the valve.

[0023] The valve 20 includes a valve disc or head 22, a tapered portion24, and a valve stem 26. An upper spring retainer 32 and a lower springretainer 34 may also be included. The valve 20 and the cylinder head 12are formed and assembled as generally well known in the art. The valveguide 18 receives the valve stem 26 and aligns the valve 20 as it movesup and down so that a tight seal is formed between the valve seat 16 andthe tapered portion 24 surrounding the valve disc 22, when the valve 20is in its closed position, as may be seen in FIGS. 1 and 4.

[0024] The electromechanical valve actuator 10 generally includes ahousing 40 defining a cavity containing electromagnets 52 and 54, anarmature stem 60, an armature 70, and a hydraulic lift mechanism 80. Theupper and lower electromagnets 52 and 54 move the armature 70 andattached armature stem 60 to drive the engine valve 20 between its openand closed positions.

[0025] The housing 40 may be formed in a variety of sizes and shapes,which may be dictated by space constraints of the internal combustionengine. The housing 40 provides structural rigidity and attaches theelectromechanical valve actuator 10 to a cylinder head 12 of an internalcombustion engine. Of course, it should be readily apparent to oneskilled in the art that a variety of means may be used to provide thestructural rigidity or method of attachment.

[0026] In the illustrated embodiment, the upper electromagnet 52 isfixed relative to the housing 40 such as by pins 42 while the lowerelectromagnet 54 is mounted within the housing 40 so that it is movablerelative to the housing 40. Suitable electromagnets are generally wellknown in the art and can have a variety of shapes that may be formedfrom the individual plates of magnetically conductive material to form alamination stack. The electromagnets 52 and 54 may include a coil ofwires 53 wound within the lamination stack. The electromagnets 52 and 54are connected to a source of electrical current (not shown) which can beselectively turned on and off independently by a controller such as anengine management system 100 (FIG. 6). An energized electromagnet 52 or54 provides magnetic force to attract the armature 70. It should readilybe recognized that a separate means may be used in place of the housing40 to hold the upper electromagnet 52 in place.

[0027] The armature 70 is mounted to move with the armature stem 60 andis located between the upper electromagnet 52 and the lowerelectromagnet 54. In the illustrated embodiment, the surfaces of thearmature 70 facing the electromagnets 52 and 54 are approximately thesame size and shape as the surfaces of the electromagnets 52 and 54facing the armature 70. Of course, it should be readily obvious to oneskilled in the art that the sizes and shapes of the armature 70 and ofthe electromagnets 50 may vary between applications.

[0028] An armature spring 62 and a valve spring 64 operably engage thevalve to urge the valve toward its open or closed positions. Thearmature spring 62 is mounted above the upper electromagnet 52 withinthe housing 40 to exert a biasing force urging the valve 20 toward itsopen position. In the illustrated embodiment, the armature spring 62 isa compression spring and is located between the armature spring retainer32 and the hydraulic lift mechanism 80. The armature spring 62 may beany compression spring known in the art for use with traditional valvesor electromechanical valves. The size, shape, and location of thearmature spring 62 may vary from application to application. A valvespring 64 is mounted, in the illustrated embodiment, between thecylinder head 12 and the valve spring retainer 34. The valve spring 64is also a compression spring as shown in the illustrated embodiment. Ofcourse, it should be readily recognized to one skilled in the art thatother placements of the springs 62 and 64 are possible and that certainplacements may also result in opening and closing of the valvesdifferently than shown in the illustrated embodiment.

[0029] The hydraulic lift mechanism 80 varies the amount of valve liftand, in the illustrated embodiment, includes a hydraulic slide 82 and ahydraulic chamber 84. The hydraulic slide 82 is formed in theillustrated embodiment in the shape of a sleeve having an upper segment72, a lower segment 74, and a passage 78 to accommodate the upperelectromagnet 52 and pins 42. The lower electromagnet 54 is attached tomove with the slide 82 by a variety of means such as a compression fit,adhesive, bonding or pins. The hydraulic chamber 84 is defined in theillustrated embodiment at the upper end of the housing 40 by the housingand the hydraulic slide 82. As the pressure in the chamber 84 is varied,the slide 82 moves relative to the housing 40. As the lowerelectromagnet 54 moves with the slide 82 and the upper electromagnet 52is fixed to the housing 40, movement of the slide 82 changes thedistance between the electromagnets 52 and 54 and the length of thevalve stroke.

[0030] In the illustrated embodiment, hydraulic fluid in the hydraulicchamber 84, such as engine oil, is pressurized by the oil pressure ofthe engine or an auxiliary pump. In some embodiments the hydraulic liftmechanism 80 may include hydraulic lines 86, hydraulic valves 88 and apump 102. The hydraulic lines 86 provide a fluid connection between thehydraulic chamber 84 and the pump 102. Hydraulic valves 88 may besituated between the hydraulic chamber 84 and the pump 102 to controlflow through the hydraulic lines 86. The hydraulic valves 88 control theheight of the hydraulic slide 82 in conjunction with the forces from thesprings 62 and 64. The hydraulic valve or valves 88 control the fluidpressure in the hydraulic chamber 84. In the illustrated embodiment, thehydraulic valve 88 is a spool valve. A spool valve is used because ituses a series of hydraulic channels to maintain a specified positionregardless of the forces acting on the slide 82. The hydraulic valve 88is controlled by the engine management system 100. The engine managementsystem 100 can easily control valve lift through existing techniques ofdetermining air flow needed to the engine. Of course, the enginemanagement system may be programmed from lab tests or road tests of whatvalve lifts are needed under specified engine operating conditions tomaximize efficiency. In the illustrated embodiment, the pump 102 is theengine oil pump and engine oil is used as the hydraulic fluid. Of coursea separate pump as well as separate hydraulic fluid may be used. Aseparate means for heating the fluid may also be included (not shown).

[0031] In operation, the valves are opened and closed as is well knownin the art for electromechanical valves. While the system is unpowered,the armature 70 is in a neutral position, approximately centered betweenthe upper and lower electromagnets 52 and 54 due to the biasing of thesprings 62 and 64. Upon start up, either the upper or lowerelectromagnet 52 or 54 is energized, attracting the armature 70, therebyopening or closing the valve 20. The power is then switched between theelectromagnets 52 and 54 causing the armature 70 to travel pole face topole face, opening and closing the valve 20. As with mostelectromechanical valves, the timing of the opening and closing may alsobe varied for more efficient engine operation.

[0032] When the valve 20 is commanded to a full open or full closedposition, the armature 70 is attracted to an electromagnet pole face. Inorder to hold the valve 20 closed enough current must be delivered tothe electromagnet pole face to produce a magnetic force larger than thespring force which acts in the opposite direction. The illustratedembodiment has the advantage that during reduced lift operation thehydraulic slide moves resulting in a lower spring force that theelectromagnet must overcome. In other words, during low lift operation,the spring force opposing the electromagnet force is reduced. Thisresults in less required electromagnet force and therefore less powerconsumption by the electromagnet when compared to a stationary full liftactuator.

[0033] The amount of valve lift during engine operation may be changedby varying the pressure in the hydraulic chamber 84 and therefore theposition of the slide 82. A low pressure causes the hydraulic slide 82to be in a reduced lift position, as shown in FIGS. 1-3. Valve spring 64exerts pressure on the slide 82, causing the slide to move upward duringlow pressure conditions such as at low rpms. Of course, other means maybe used to exert pressure on the hydraulic slide 82 to move the slide 82to a reduced lift position such as an additional spring or an oilpocket. The reduced valve lift allows for optimized throttless engineoperation through all ranges.

[0034] As the engine revolutions increase, more flow is needed to andfrom the cylinders for the engine to operate efficiently and at thedesired power levels. Engine oil pressure increases as the revolutionsincrease and pushes the hydraulic slide 82 downward to a desired lift,as shown in FIGS. 4 and 5, at the maximum lift. When the hydraulic slide82 moves downward so does the lower electromagnet 54, causing thearmature to travel a greater distance between the upper and lowerelectromagnets 52 and 54. It should readily be seen that because thehydraulic slide 82 compresses or relaxes spring 62, the armature 70,when at rest, is centered between the upper and lower electromagnets 52and 54, no matter what lift is being provided.

[0035] To provide more precise control over the valve lift, thehydraulic lifting mechanism 80 may use the hydraulic valves 88 andseparate oil pump 102. A separate hydraulic pump 102 also can be helpfulto provide full valve lift in any engine operating conditions. Forexample, a separate pump 102 is useful at low rpms where lots of torqueis needed, such as pulling a heavy trailer, to increase valve lift andallow more flow. The hydraulic valves 88 may reduce valve lift at higherrpm conditions where little power is needed from the engine, forexample, during operation at constant speeds such as operation of avehicle on the highway.

[0036] In operation, the above electromechanical valve also allows forthrottless operation. The variability of the valve lift and timingallows the amount of air entering the cylinder to be controlled withouta throttle body or throttle plate. This allows the piston to pull inatmospheric pressurized air, thereby increasing engine efficiency.

[0037] The foregoing discussion discloses and describes an exemplaryembodiment of the present invention. One skilled in the art will readilyrecognize from such discussion, and from the accompanying drawings andclaims that various changes, modifications and variations can be madetherein without departing from the true spirit and fair scope of theinvention as defined by the following claims.

What is claimed is:
 1. An electromechanical valve comprising: a firstelectromagnet; a second electromagnet spaced from said firstelectromagnet; and a hydraulic lifting mechanism coupled to one of saidfirst and second electromagnets to change the spacing between said firstelectromagnet and said second electromagnet.
 2. The electromechanicalvalve of claim 1 further comprising a housing and wherein said hydrauliclifting mechanism further includes a hydraulic slide moveable relativeto said housing, said first electromagnet being fixed to said housingand said second electromagnet being fixed to said hydraulic slid.
 3. Theelectromechanical valve of claim 2 wherein said hydraulic slide and saidhousing define a pressure chamber, said pressure chamber containingfluid that exerts a pressure on said hydraulic slide, said hydraulicslide being moveable in response to said pressure.
 4. Theelectromechanical valve of claim 2 wherein said first electromagnet ispositioned vertically above said second electromagnet.
 5. Theelectromechanical valve of claim 2 further including a pin attachingsaid first electromagnet to said housing and a passageway defined insaid hydraulic slide, said pin passing through said passageway.
 6. Theelectromechanical valve of claim 1 further including a first springpositioned between said first electromagnet and said hydraulic liftingmechanism.
 7. The electromechanical valve of claim 1 further comprisinga second spring and a cylinder head, said second spring being locatedbetween said cylinder head and said lower electromagnet.
 8. Theelectromechanical valve of claim 1 further including an armature havinga neutral position, said first spring and said second spring exerting afirst pressure and a second pressure on said armature in said neutralposition, said first pressure and said second pressure approximatelycentering said armature between said first electromagnet and said secondelectromagnet at said neutral position.
 9. An electromechanical valvefor an internal combustion engine comprising: an upper electromagnet; alower electromagnet spaced from said upper electromagnet, a hydraulicslide coupled to said lower electromagnet to change the spacing betweensaid lower electromagnet and said upper electromagnet.
 10. Theelectromechanical valve of claim 9 further including an actuator stem,said upper and lower electromagnet surrounding a portion of saidactuator stem.
 11. The electromechanical valve of claim 10 furtherincluding an armature attached to said actuator stem, said armaturebeing located between said upper electromagnet and said lowerelectromagnet.
 12. The electromechanical valve of claim 9 furtherincluding a housing defining a defining a fluid chamber containing afluid that exerts a pressure on said slide, said slide moving relativeto said housing in response to said pressure.
 13. The electromechanicalvalve actuator of claim 12 further including a hydraulic pump in fluidcommunication with said fluid chamber, said hydraulic pump changing afluid pressure in said fluid chamber.
 14. The electromechanical valveactuator of claim 12 further including a cylinder head and valve stemhaving an open position with a lift relative to said cylinder head, saidlift being proportional to said pressure.
 15. An internal combustionengine having a variable lift electromechanical valve comprising; anupper electromagnet; a lower electromagnet spaced from said upperelectromagnet; and a hydraulic positioning means connected to said lowerelectromagnet to change the spacing between said upper electromagnet andsaid lower electromagnet.
 16. The internal combustion engine of claim 15wherein said hydraulic positioning means includes a fluid chambercontaining a fluid that exerts a pressure on a hydraulic slide, saidhydraulic slide moving said lower electromagnet relative to said upperelectromagnet in response to said pressure.
 17. The internal combustionengine of claim 17 wherein said fluid exerts a first pressure and asecond pressure, said first pressure having a first spacing between saidupper electromagnet and said lower electromagnet, said second pressurehaving a second spacing between said upper electromagnet and said lowerelectromagnet.
 18. The internal combustion engine of claim 17 wherein ifsaid second pressure is greater than said first pressure then saidsecond spacing is greater than said first spacing.
 19. The internalcombustion engine of claim 17 wherein as said pressure increases saidspace between said upper electromagnet and said lower electromagnetincreases.
 20. The internal combustion engine of claim 19 furthercomprising an upper spring and a lower spring, said upper spring andsaid lower spring exerting a first spring pressure and a second springpressure, said first spring pressure and said second spring pressureincreasing as said pressure increases.